An intrusion is when something breaks in without permission, and in this case it is virus. for a secure network it is important that a computer holds anti-intrusion software that prevents hackers and virus from gainning access. this will allow a computer to be safe and hold its information that others will not be able to access. virus in this case makes computer malfunction, a virus can intrude in your computer when you very least expect it. a certain website, or downloading files can cause this intrusion. this is like an direct contact to the computer that can only make the intrusion fully possible. a compter getting affected by a virus is no different than a person getting a virus. a computer can easily be vonurable when a removeable data tranfering device is installed and that device contains that virus, chances are then high that the intrusion will take place.